UNIT IV

JET PROPULSION

SYLLABUS

(X)* First halfTheory of jet propulsion - ram jet, turbojet, turbofan and turbo propengines(Y)*Second HalfOperating principle, cycle analysis and use of stagnation state performanceof engines. Thrust equation – Thrust power and propulsive efficiency

PART – A

IIVVXX11.. What are the benefits of thrust augmentation in a turbojet engine?

IIVVXX22.. What is the significance of low and high TSFC in jet propulsion?

IIVVXX33.. What is the type of compressor used in turbo jet?

IIVVXX44.. Why ramjet engine does not require a compressor and a turbine?

IIVVXX55.. Define thrust power of aircraft engine.

IIVVXX66.. List out the different types of jet engines.

IIVVXX77.. Give the components of turbo jet.

IIVVXX88.. Define propeller engine and jet engine.

IIVVXX99.. What is the difference between shaft propulsion and jet propulsion?

IIVVXX1100.. What is turbo prop unit?

IIVVXX1111.. What is ram effect?

IIVVXX1122.. Explain specific thrust as applied to jet engines.

IIVVXX1133.. Differentiate between pressure thrust and momentum thrust.

IIVVXX1144.. What is thrust augmentation?

IIVVXX1155.. Why after burners are used in turbojet engine?

IIVVXX1166.. What are the effects of forward speed and altitude in the case of propulsion?

IIVVXX1177.. What are the advantages of ram jet?

IIVVXX1188.. What are the main parts of ramjet engine?

IIVVXX1199.. Name three commonly used aircraft engines.

IIVVXX2200.. How is turbofan engine different from turboprop engine?

IIVVXX2211.. What are the various types of breathing engine?

IIVVXX2222.. What is a bypass engine end define bypass ratio

IIVVYY11.. Find the ratio of jet speed to flight speed for optimum propulsive efficiency.

IIVVYY22.. A turbojet engine having a flight velocity of 800 km/hr at an ambient pressure of 60 kPa,

the properties of gas entering the nozzle are 300 kPa and 2000C. The mass flow rate of air

is 20 kg/s. Assuming for air Cp/Cv = 1.4 and R = 0.287 kJ/kgK. Find the thrust power of

the engine.

IIVVYY33.. Find the optimum propulsive efficiency when the jet velocity is 500 m/s and flight

velocity is 900 m/s.

IIVVYY44.. Draw T-S diagram of ideal and actual brayton cycle and bring out the differences

between them.

IIVVYY55.. Define propulsive efficiency.

IIVVYY66.. Define thrust for a rocket engine and how it is produced.

IIVVYY77.. What is specific impulse?

IIVVYY88.. Define speed ratio in propulsive system.

PART – B

IIVVXX11.. (i) Differentiate turbojet and turboprop propulsion engines with suitable diagrams.(ii) Write the equations to calculate propulsive efficiency and thermal efficiency of anaircraft.

IIVVXX22.. Explain with sketches the working of the by-pass engine. How thrust equation is derivedfor bypass engine? What are the merits and demerits of such engines over itscompetitors?

IIVVXX33.. How is forward motion of an aircraft achieved by propeller action? How does the aircraftlift-off the ground? Explain with the help of illustrative sketches.

IIVVXX44.. Derive an expression for the air-standard efficiency of a turbojet engine in terms of thepressure ratio. Depict graphically its variation with the temperature ratio.

IIVVXX55.. (i) Draw a neat sketch of a supersonic diffuser for a ramjet engine with oblique andnormal shocks.(ii) Depict variation of static pressure through the diffuser from its entry to exit.

IIVVXX66.. Explain with neat sketches the principle of operation of (i) Turbofan engine and (ii)Turbojet engine.

IIVVXX77.. Explain the working principle of the ramjet engines with neat sketch and state itsadvantages and disadvantages.

IIVVXX88.. Derive the expressions for the jet thrust, propeller thrust, propulsive efficiency, thermalefficiency, overall efficiency and the optimum value of flight to jet speed ratio for aturbojet engine.

IIVVXX99.. Derive the following relations for aircraft engine

Flight to jet sped ratiojacm

F 1

Thrust in a turbojet engine eaeeaja AppucmucmF )()()(

IIVVYY11.. A turbojet engine operating at a mach number of 0.8 and the altitude is 10 km has thefollowing data. Calorific value of the fuel is 42,800 kJ/kg. Thrust force is 50 kN, massflow rate of air is 45 kg/s, Mass flow rate of fuel is 2.65 kg/s. Determine the specificthrust, thrust specific fuel consumption, jet velocity, thermal efficiency, propulsiveefficiency and overall efficiency. Assuming the exit pressure is equal to ambient pressure.

IIVVYY22.. A jet propelled aircraft flying at a mach number 0.6 at an altitude of 5.0 km inducts air ata rate of 20 kg/s. The diffuser recovery is 0.9. The compressor pressure ratio is 5.0 andthe maximum total temperature in the cycle is 1300 K. The gases expand in the nozzle toa pressure of 0.7 bar. The isentropic efficiencies of the compressor, turbine and nozzleare 0.8, 0.85 and 0.92 respectively. The calorific value of the fuel is 44 MJ/kg. Assumethat the products of combustion have the same properties as that of air. Calculate (i) Air-fuel ratio (ii) Power output of turbine (iii) Exhaust jet velocity (iv) Engine thrust and (v)Overall efficiency.

IIVVYY33.. An aircraft propeller flies at a speed of 440 kmph. The diameter of the propeller is 4.1 mand the speed ratio is 0.8. The ambient conditions of air at the flight altitude are T = 255Kand P = 0.55 bar. Find the following: (i) Thrust (ii) Thrust power and (iii) Propulsiveefficiency.

IIVVYY44.. A ramjet engine propels an aircraft at a Mach number of 1.4 and at an altitude of 6000 m.The diameter of the inlet diffuser entry is 40 cm and the calorific value of the fuel is 43MJ/kg. The stagnation temperature at the nozzle entry is 1500 K. The properties of thecombustion gases are same as those of air. ( = 1.4, R = 287 J/kg K). Determine the

following:1. The efficiency of the ideal cycle,2. Flight speed,3. Air flow ratio,4. Diffuser pressure ratio,5. Fuel air ratio,6. Nozzle pressure ratio,7. Nozzle jet Mach number,8. Propulsive efficiency and9. Thrust. Assume diffuser efficiency ƞD = 0.92, Combustion efficiency ƞB = 0.97

and nozzle jet efficiency ƞN = 0.95. Stagnation pressure loss in the combustionchamber = 0.02 P02.

IIVVYY55.. An aircraft flies at 90 km/hr. One of its turbojet engines takes in 40 kg/s of air andexpands the gases to the ambient pressure. The air-fuel ratio is 50 and the lower calorificvalue of the fuel is 43 MJ/kg. For maximum thrust power determine:

1. Jet velocity,2. Thrust,3. Specific thrust,4. Thrust power,5. Propulsive, thermal and overall efficiencies.

IIVVYY66.. A turbojet plane has two jets of 250 mm diameter and the net power at the turbine is 3000kW. The fuel consumption per kWhr is 0.42 kg with a fuel of calorific value 49 MJ/kg,when flying at a speed of 300 m/s in atmospheric having a density of 0.168 kg/m3. Theair fuel ratio is 53. Calculate (i) Absolute velocity of jet, (ii) Resistance or Drag of theplane (iii) Overall efficiency of the plane and (iv) Thermal efficiency.

IIVVYY77.. A turbojet engine operates at an altitude of 11 km and a Mach number of 0.82. The datafor an engine is given below: Stagnation temperature at the turbine inlet = 1220 K,Stagnation temperature rise through the compressor = 170 K, Calorific value of the fuel= 42 MJ/kg, Compressor efficiency = 0.75, Combustion chamber efficiency = 0.96 andspecific impulse = 20 seconds. Determine (i) Air fuel ratio, (ii) Compressor pressureratio, (iii) Turbine pressure ratio, (iv) Exhaust nozzle pressure ratio and (v) Mach numberof exhaust gas.

IIVVYY88.. The diameter of the propeller of an aircraft is 2.5 m. It flies at a speed of 500 kmph at analtitude of 8000 m. For a flight to jet speed ratio of 0.75 determine,

1. The flow rate of air through the propeller,2. Thrust produced,3. Specific thrust,4. Specific impulse and5. The thrust power.

IIVVYY99.. A turbojet engine operating with its exhaust nozzle unlocked propels an aircraft at auniform speed of 900 km/h when it develops a thrust of 14 kN. The air intake to theengine is 50 kg/s and its air fuel ratio is 85. The calorific value of the fuel supplied to theengine is 44000 kJ/kg. The isentropic enthalpy change in the nozzle is 150 kJ/kg. Findthe thrust power, propulsive power, propulsive efficiency, thermal efficiency and overallefficiency of the engine.

IIVVYY1100.. A turbojet aircraft flies at 850 km/h at an altitude of 10000 m above the mean sea level.The diameter of the inlet section and the jet exit are 0.75 m and 0.5 m respectively. Thepressure and velocity of the gases at the exit are 0.3 bar and 500 m/s. The air fuel ratio forthe engine is 40. Calculate (i) air flow rate through the engine (ii) thrust (iii) specificthrust (iv) fuel specific impulse (v) thrust power and (vi) TSFC.